But Chris Herbst of Arizona State University and John Ifcher of Santa Clara University noticed some weaknesses in earlier studies on the phenomenon. Why did the studies always treat the happiness gap as a constant? Also, why was the word parents always defined as people whose egg and sperm had met and created a child? This excluded a segment of society who chose to have children: adoptive parents, step-parents, relatives who take in children—non-biological parents who willingly (and many times, happily) take in children to raise because they want to and, perhaps, find joy in having kids around.

Their results, appearing in a study titled "The Increasing Happiness of Parents," challenge previous research on parental happiness: While parents appear to remain just as happy as they did back in the 1980s, the happiness of non-parents has fallen. This means that, today, parents are happier relative to non-parents—a shift from previous evidence.

Ifcher explained the results this way: “What we believe is going on is that there is a general negative trend in happiness among adults—[but] that negative trend is not happening for parents.” Adults seem to be getting grumpier as a whole, but parents are bucking that general trend.

The findings stay “sturdy” even in the face of common tough childrearing times, such as the terrible twos and adolescent angst, surprising Herbst and Ifcher.

“Parents with young kids of any age are becoming happier than non-parents,” Herbst told me. “It doesn’t matter how old the child is in the household: Parents with kids in any of these age groups are becoming happier.”

Herbst and Ifcher also tested their findings against the idea that having fewer kids would lead to happiness: Is there a peak number of children that a parent could have to experience for maximum happiness before there was a diminishing marginal utility in happiness? Not so, it seems. Additionally, their findings held even for the least happy subgroup of parents: single working mothers. Their discovery? Moms and working moms are becoming happier relative to their childless counterparts.

“It speaks potentially to the role of technology,” Herbst said, noting that the prevalence of washing machines, kitchen appliances, and other aides to household chores have allowed for working mothers to focus more on their children and enjoy it.

In short, “it’s remarkable” how just the presence of children seems to protect against declining happiness, Ifcher said.

Herbst and Ifcher offer three theories why parents are becoming happier—and what that means for American society.

First, there’s the phenomenon that Robert Putnam identified in his 2000 book Bowling Alone—that Americans were becoming increasingly isolated from community and family. Herbst and Ifcher argue that families are the “last vestige of community life in American society.”

“Parents are more likely to spend time with friends, get the news, be interested in politics, think people are honest, have faith in the economy, be trusting,” Herbst said. “We think that parents remain better attached to society, and we think the linchpin of that attachment is kids.”

Moreover, contrary to the notion that kids hinder the social lives of mom and dad, children help parents stay social. Think PTA meetings, playdates with fellow parents in tow, and taking part in the sociopolitical fabric of the neighborhood.

Second, the financial hardship brought on by children has lessened over time. The U.S. now has a more generous earned income tax credit and childcare tax credits, which means parents have more of a financial cushion than they used to.

“The social safety net has begun to favor parents more over time than non-parents,” Herbst said. In short: “Parents may have more money in their pocket, and more money translates to more happiness.”

Finally, who is having a kid these days is different than who had children in previous decades—and their reasons for doing so have changed. Median marriage ages are increasing, and having a birth out of wedlock isn’t as socially frowned upon as it used to be.

In other words, parents are probably becoming parents because they want to be parents, and less because of societal pressure. These adults are more likely to be a self-selected group, desire their children, and therefore derive more happiness from having the children they wanted.

“The composition of parents and non-parents looks different,” Herbst said, calling the comparison of who was a parent in the 1970s to who is a parent today an apples and oranges comparison. “Who is choosing to become a parent and who is choosing to remain childless have changed,” he said. “Parents look a lot different today."

And as far as these researchers are concerned, they're looking a lot happier.